diff --git a/example/lib/03_2_depends_on_async/depends_on_async_sample.dart b/example/lib/03_2_depends_on_async/depends_on_async_sample.dart
index 8a5c6d5..a17b89e 100644
--- a/example/lib/03_2_depends_on_async/depends_on_async_sample.dart
+++ b/example/lib/03_2_depends_on_async/depends_on_async_sample.dart
@@ -16,6 +16,7 @@ class DependObservableAsyncSampleLayoutState
   late Telescope<int> weight;
   late Telescope<double> bmi;
   late Telescope<String> showingText;
+  var  loadingBMI = Telescope(false);
 
   @override
   void initState() {
@@ -26,11 +27,12 @@ class DependObservableAsyncSampleLayoutState
 
     bmi = Telescope.dependsOnAsync(0, [height, weight], () async {
       return await calculateBMI(height.value, weight.value);
-    });
+    }, isCalculating: loadingBMI);
 
-    showingText = Telescope.dependsOn([height, weight, bmi], () {
+    showingText = Telescope.dependsOn([height, weight, bmi, loadingBMI], () {
       var bmis = bmi.value.toString();
-      bmis = bmis.length > 5 ? bmis.substring(0, 5) : bmis;
+      bmis = loadingBMI.value ? "..." : bmis.length > 5 ? bmis.substring(0, 5) : bmis;
+
       return "weight is ${weight.value} and height is ${height.value} so bmi will be $bmis";
     });
   }
diff --git a/lib/src/telescope.dart b/lib/src/telescope.dart
index b346afe..72c9944 100644
--- a/lib/src/telescope.dart
+++ b/lib/src/telescope.dart
@@ -46,15 +46,22 @@ class Telescope<T> {
   /// Use this if you need to use await in calculate function
   Telescope.dependsOnAsync(
       this.holden, List<Telescope> dependencies, Future<T> Function() calculate,
-      {this.iWillCallNotifyAll = false}) {
+      {
+        this.iWillCallNotifyAll = false,
+        Telescope<bool>? isCalculating,
+      }) {
+    isCalculating?.value = true;
     calculate().then((value) {
       holden = value;
+      isCalculating?.value = false;
       notifyAll();
     });
     for (var o in dependencies) {
       o.subscribe(() {
+        isCalculating?.value = true;
         calculate().then((value) {
           holden = value;
+          isCalculating?.value = false;
           notifyAll();
         });
       });